NESDIS News & Articles

Top 5 Terms You Should Know for a Satellite Launch

“T- 3..2..1..Liftoff!” As we head toward launch, all eyes and ears will be on NOAA’s GOES-R satellite atop its Atlas V 541 rocket. Make sure you are caught up on launch day lingo so that you can follow along!

Here is a list of the top five most common, but perhaps misunderstood, terms, abbreviations and phrases you might hear during the GOES-R satellite launch. Once you know what they mean, follow the launch on Twitter @NOAASatellites!

1. L- and T-

L- (pronounced "L minus”) refers to the days, hours, and minutes remaining in the scheduled countdown to launch, which occurs at L-0. The “L” stands for launch.

T- (pronounced "T minus”) refers to the time remaining on the official countdown clock. The “T” stands for time. During planned holds in the countdown process (when the countdown clock is intentionally stopped), the T- time also stops. The L- time, however, is synced to the clock on the wall and continues to advance.

Under normal conditions, these countdowns remain in sync. For example, there is a 15 minute hold planned at T-4 minutes, which occurs at L-19 minutes. Once the hold is lifted and the countdown resumes, the clocks will be synced and show 4 minutes remaining.

2. Atlas V Rocket

GOES-R will be going to space aboard a stacked "two stage” rocket called a ULA Atlas V 541 Expendable Launch Vehicle (ELV). Two stages means that the rocket has two sections, or stages, that are mounted on top of each other. Each stage has its own fuel and its own engine. Each stage is ejected into space once its job is done and all the fuel is spent.

The Atlas V Common Core Booster, or rocket, is the first stage of the Atlas V 541 ELV. This booster will ignite first and is the main engine powering the vehicle’s ascent. This stage carries the spacecraft through the first leg of its journey, ending in a geostationary transfer orbit.

3. Centaur Upper Stage

This is the second stage of the Atlas V rocket and is considered the vehicle's "brains." It is designed to power the second leg of the satellites trip, placing it into a geostationary orbit. The satellite will then separate from the Centaur Upper Stage and complete the final maneuvers on its own, placing itself in a designated location in geostationary orbit.

4. Liftoff

Liftoff denotes the exact moment when the rocket, with the satellite onboard, begins to leave the launch pad under its own power, beginning its journey to space.

5. MES “Main Engine Start” and MECO “Main Engine Cut-Off”

MES refers to the moment when the Centaur Upper Stage’s main engine begins to fire, or burn. GOES-R will go through three main engine starts on its way to geostationary orbit, designated MES1, MES2 and MES3.

MECO refers to the moment when the Centaur Upper Stage has completed a main engine burn and cuts off, entering a coasting phase. GOES-R will go through three main engine starts and cut-offs on its way to geostationary orbit. They are identified as MECO1, MECO2 and MECO3.